Very simple once one knows. Or the fact that Poser/SuperFly applies gamma correction to a color that I plug into a value input, so I have to reverse that in a math node.

I just use the texture node gamma correction options, if I'm understanding you correctly, 2.2/custom 1 alpha. Unless the render has some poor lighting it's pretty consistent results across software and devices. I check my work across different displays, my tablet being a bit more contrasty of a display than my computer. Usually auto contrast in photoshop results in no visible adjustment from most poser renders unless I really hastily lit it or the global illumination is poorly set. OpenGL preview render stuff I tweak in photoshop if necessary.